在Rails中查询联接关联

Question

Campaign have attributes :start_date,:end_date

Invoice have attributes :start_date,:end_date

campaign.rb

has_many:invoices

invoice.rb

belongs_to:campaign

I want to get all those cmapaigns whose start_date is less than current date AND whose end_date is between campaign.invoices.last.created..current_date

How I query for this?

Answer 1

Try this:

 Compaign.joins(:invoices)
            .where("compaigns.start_date < :today AND compaigns.end_date < :today", today: Date.today)
            .group("compaigns.id")
            .having("compaigns.end_date > MAX(invoices.created_at)")

Answer 2

I never used Rails magic to perform more-or-less complicated requests against database. It always results in drastic overhead, N+1 queries, or some unexpected penalties. Here is the plain old good SQL version to perform this task:

Campaign.connection.execute <<-SQL
   SELECT campaigns.*, last_invoice_date
   FROM campaigns 
     JOIN (
       SELECT invoices.campaign_id AS campaign_id,
              MAX(invoices.started) AS last_invoice_date
       FROM invoices
       GROUP BY invoices_campaign_id
     ) AS last_invoices
     ON (last_invoices.campaign_id = campaigns.id)
     WHERE campaigns.start_date < NOW()
       AND campaigns.end_date < NOW()
       AND campaigns.end_date >= last_invoices.last_invoice_date
SQL.to_a

The above was not tested for the obvious reason, but it should work either as is or with slight modifications.

Answer 3

campaigns = Campaign.where("DATE(start_date) < ?", Date.today).includes(:invoices)

invoices = campaigns.each do |campaign|
              campaign.invoices.where("Date(campaigns.end_date)" BETWEEN campaign.invoices.last.created_at.to_date AND Date.today)
           end

invoices.map(&:campaign)